arrangements: Fast Generators and Iterators for Permutations, Combinations and
Partitions

Fast generators and iterators for permutations, combinations
and partitions. The iterators allow users to generate arrangements in
a memory efficient manner and the generated arrangements are in
lexicographical (dictionary) order. Permutations and combinations can
be drawn with/without replacement and support multisets. It has been
demonstrated that 'arrangements' outperforms most of the existing
packages of similar kind. Some benchmarks could be found at
<https://randy3k.github.io/arrangements/articles/benchmark.html>.